Long-range electron transfer in pilus nanowires

Gemma Reguera

Microbiology and Molecular Genetics - Michigan State University

Geobacter bacteria gain energy for growth by transferring metabolic electrons to insoluble electron acceptors using conductive protein appendages or pili. This process can be harnessed for the bioremediation of toxic metals and electricity production in microbial electrochemical cells. Key to these applications is knowledge of how the pili conduct electrons. The pili lack redox cofactors, yet conduct electrons along µm lengths at rates that greatly exceed the cellular rates of respiration. Their rectifying properties allow them to function as electronic conduits between the cell and the electron acceptor. Evidence to date supports the notion of a hybrid pathway for electron transfer along the pilus nanowire that integrates a tunneling regime through intermolecular contacts and intramolecular electron hopping. The pathways involve specific amino acids of the pilin and are optimized by the pilin’s structure and polarization. Thus, Geobacter pili serve as a new paradigm in biological electron transfer with the potential to provide novel insights and challenge current dogmas about protein electron transfer. This knowledge is critical for the development of improved biological fuel cells and bioremediation processes as well as for the design of protein-based nanoelectronic devices.